This invention relates to an exposure apparatus for projecting a pattern onto a photosensitive substrate and, more particularly, to a substrate adjuster and a substrate holder, which are used in such an exposure apparatus to allow different types of substrates having different thicknesses to be appropriately exposed to exposure light, and to a method for holding such substrates.
In conventional exposure apparatuses, the driving range of a Z-stage (Z-direction stage) is set to a prescribed range so as to correspond to a certain range of thicknesses of the substrate used. In this case, when a pattern is projected onto a different type of substrate whose thickness is different from that of the previously used substrate, the substrate holder, which is fixed onto the Z-stage to hold a substrate, must be replaced with another one that is suited for the thickness of the new substrate. If the same substrate holder is used for the new substrate having a different thickness, the vertical position (i.e., the height) of the substrate surface may deviate from the image plane of the projecting lens system beyond the driving range of the Z-stage. In such a case, the substrate surface cannot be brought into the image plane by simply driving the substrate stage (Z-stage) in the vertical direction.
For example, a silicon wafer typically has a thickness of 0.5 mm, and a ceramic substrate has a thickness of 1 mm to 3 mm. When a pattern is transferred onto a silicon wafer through the exposure process, a relatively thick substrate holder is used. On the other hand, for a ceramic substrate, a substrate holder which is relatively thin is used. These examples are illustrated in FIGS. 5(A) and 5(B). In FIG. 5(A), a relatively thin holder 104 is fixed onto the substrate stage 102 to hold a ceramic substrate 100 by means of adsorption. In FIG. 5(B), a silicon wafer 106 is held by a relatively thick holder 108 through adsorption on the substrate stage 102. These substrate holders are usually screwed on the substrate stage 102. By using different substrate holders having different thicknesses, the substrate surface can be reliably brought into the image plane.
In this method, however, substrate holders must be screwed onto and off of the substrate stage 102 every time one holder is replaced with another. This replacement is troublesome and time-consuming, which causes the productivity of the exposure apparatus to drop. Furthermore, during the interchange of the substrate holders, the projection lens may be damaged, or dust may adhere onto the substrate stage, which adversely affects the precision of the pattern transfer and the image quality.